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Tips on reducing ripple voltage on linear regulator

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sahko123:
This isn't a microphone pre-amp supply but a headphone power supply, still requires low noise and ripple. My definition for dropout voltage is the minimum difference between input and output so if under load the negative peak of the input ripple from the rectifier and reservoir capacitors drops to 14V and you have a drouput voltage of 4V then the regulator will go down to 10v and follow the input ripple on its way back up but if the dropout is lower the input voltage can go lower without affecting the output voltage as much

Ian.M:
The dropout voltage is constrained by several things.  The capacitance multiplier drops about 0.9V, the current mirror output side drops about 0.3V Vce + the drop across its emitter resistor, and finally the pass transistor Darlington pair contributes two Vbe drops so about 1.3V.  Reducing the emitter resistors R6 and R7 to 100R will save you maybe half a volt.  The action of D5 to lift the supply to the current mirror is much more important because it means at high load currents, if the ripple is over about two volts, the dropout voltage is reduced to the min. Vce drop of the Darlington of about 1V.

It isn't in any way constrained by my choice of reference voltage - I could re-jig the circuit with 4.7V Zeners, and if I kept the tail current the same, the only side effects would be an increase of the min. output voltage to 9.4V and, I think, slightly poorer regulation with respect to load current due to the lower 'headroom' for the long-tailed pair.

N.B. the exponential voltage source I used in the sim to approximate the ripple doesn't model the ripple increasing with load current, nor of course does it model transformer regulation.   OTOH it does permit a DC operating point to be found, permitting AC analysis for the frequency response of the PSRR and load regulation.  One issue that will crop up if you attempt to edit V1 in its Specialized Component Editor is it will loose the the extra (seventh) parameter 10m which sets the repetition rate of the ripple. To avoid this edit its value, currently:

--- Code: ---EXP(17.4 18.6 0 0.2m 0.4m 3m 10m )
--- End code ---
and reinsert the 10m just inside the closing parentheses.  See https://www.analog.com/en/technical-articles/ltspice-using-time-dependent-exponential-sources-to-model-transients.html for the extra EXP() parameters and general hints on pulse modelling using EXP() sources.[/i]

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